Redox processes occur whenever electrons enter or leave molecular frontier orbitals. Consequently, for a given molecule, the energy and intensity of absorption and emission of electromagnetic radiation, as well as its electrical and magnetic properties, vary when electrons are added or removed. The redox process is determined to a large extent by the type, number and arrangements of atoms, i.e., by the molecular structure. The kinetics of electron transfer, induced by an external source such as an electrode, while influenced by the particular molecular structure of a material, could be controlled by the rate of potential variation at the electrode. This principle is used, for example, in variable scan rate cyclic voltammetry, to add or remove electrons at rates that may exceed chemical transformations at the surface of electrodes.
Electrochromism refers to reversible changes in optical absorption induced by electron-transfer, changes that could occur in the ultraviolet, visible or infra-red spectral regions. Electrochromism results in both color and transparency changes. Simultaneous changes in electrical and magnetic properties may also occur. The changes could occur at time scales ranging from essentially infinite (static) for a one time switch to sub seconds (dynamic) for a modulated electron transfer range. Redox active molecules (transducers) are generally effective in supporting the noted modulated changes.
Phthalocyanines are highly conjugated macrocycles known in the art, and can be used as reversible electron acceptors. Phthalocyanines also undergo electrochromism. FIG. 1 is representative of a class of highly fluorinated phthalocyanine molecules exhibiting large molar extinction coefficients, ˜105, in the UV-visible range, high thermal and chemical stability, and reversible redox properties. The organic moieties of these molecules are diamagnetic, but the introduction of metal ions with open electronic shells renders them paramagnetic. The addition or removal of electrons changes the magnetic state depending upon the type of metal and number of electrons. The electrical properties, such as conductivity, dielectric constants, etc., also vary.
Based on their unique electrochemical, optical, chemical, and electrical properties, phthalocyanines find a broad range of uses from medicine to fuel cells to advanced materials. Literature discussions addressing the properties of phthalocyanines include “Phthalocyanines: Properties and Applications” Vols. 1-4 (Eds.: C. C. Leznoff, A. B. P. Lever), VCH Publishers, New York, 1990-1996, and “Phthalocyanine Materials: Synthesis, Structure and Function” N. B. McKeown, Cambridge University Press, Cambridge, 1998. More particularly, phthalocyanines are used for their electrochemical properties in fuel cells and batteries, chemical properties in deodorants and catalysis, electrical properties in organic semiconductors and synthetic metals, and optical properties in pigments, optical disks, non-linear optics, high density memory, and photodynamic therapy of cancer. Moreover, phthalocyanines are used for their combined electrochemical and optical properties in electrochromic displays, combined optical and electrical properties in photocopier charge generators and solar cells, and combined chemical and electrical properties in chemical sensors.
Despite their favorable thermal and electronic properties, the presence of C—H bonds renders phthalocyanines chemically vulnerable. Another disadvantage of phthalocyanines is that they are sparingly soluble, which presents difficulties in processing in solution form. In particular, the poor solubility of phthalocyanines makes difficult coating of metal surfaces. Organic substituents or axial ligands that are equatorially coordinated by the macrocycle are known to enhance the compatibility of phthalocyanines with organic matrices, but at the expense of chemical stability.
Phthalocyanines can accommodate almost any metal ion at their center, thus providing opportunities for reversible electronic population of“d” and “f” orbitals. Regarding electronic properties, the orbital levels in general and the HOMO-LUMO gap in particular, are functions of both the nature of the metal center and organic moiety, thus offering prospects for rational color tuning. Fluorescence and luminescence are additional tunable optical properties, as well as the magnetic and electrical properties.
Phthalocyanines also exhibit nonlinearity of their optical properties. Phthalocyanines and their metal complexes exhibit favorable third-order nonlinear optical properties in the visible and near IR regions, which is of interest in civilian and military applications (optical limiters), as discussed in “Lead phthalocyanine reverse saturable absorption optical limiters,” J. S Shirk et al., Pure Appl. Opt., 5, 701,1996. Nonlinear absorption is the main mechanism near the limiting threshold. The spectral window over which the limiter operates can be engineered by altering both the main ring (non-peripheral) and peripheral substitution of the molecules.
From an electronic perspective, for each well-defined orbital level set, i.e., well defined energy levels of phthalocyanines, the number of electrons may be varied by the application of a variable potential using electrodes. The voltages required for electron transfer are quite low, and are generally below 5 V. Modem electronic devices are able to generate voltage sign reversals with very high frequency.
U.S. Pat. No. 6,511,971 to S. M. Gorun discloses substituted phthalocyanine compounds including perfluoroalkyl metallo perfluoro-phthalocyanine compounds and methods of synthesizing these compounds. Pharmaceutical compositions comprising substituted phthalocyanine compounds and methods of using these compounds, for example for treatment of cancer, are also disclosed. U.S. Pat. No. 6,511,971 is incorporated herein by reference in its entirety.
Additional literature references of background interest for purposes of the present disclosure include: “Introduction of Bulky Perfluoroalkyl Groups at the Periphery of Zinc Perfluoro Phthalocyanine: Chemical, Structural, Electronic, and Preliminary Photophysical and Biological Effects,” B. A. Bench, A. Beveridge, W. M. Sharman, G. J. Diebold, J. E. van Lier, S. M. Gorun, Angew. Chem. Int. Ed., 41, 748, 2002; “Effects of Peripheral Substituents and Axial Ligands on the Electronic Structure and Properties of Iron Phthalocyanine,” M.-S. Liao, T. Kar, S. M. Gorun, S. Scheiner Inorg. Chem., 43, 7151, 2004; “Spectroscopy and Electronic Structure of Electron Deficient Zinc Phthalocyanines,” S. P. Keizer, W. J. Han, J. Mack, B. A. Bench, S. M. Gorun, M. J. Stillman, J. Am. Chem. Soc., 125, 7067, 2003; “Synthesis and structural characterization of non-planar perfluoro phthalonitriles,” S. M. Gorun, B. A. Bench, G. Carpenter, M. W. Beggs, J. T. Mague, H. E. Ensley, J. Fluorine Chem., 91, 37, 1998; “Synthesis and Structure of a Bi-concave Perfluoro Cobalt Phthalocyanine and its Catalysis of Novel Oxidative Carbon-Phosphorus Bonds Formation using Air,” B. A. Bench, W. W. Brennessel, H.-J. Lee, S. M. Gorun, Angew. Chem. Int. Ed. Eng, 41, 751, 2002; and “Dome-distortion and fluorine-lined channels: synthesis, and molecular and crystal structure of a metal- and C—H bonds-free fluorophthalocyanine,” H. Lee, W. Brennessel, J. Lessing, W. Brucker, V. Young Jr., S. M. Gorun, Chem. Commun., 1576, 2003.
Despite efforts and investigations to date, a need remains for phthalocyanines that offer enhanced properties and/or support desired applications. In addition, a need remains for coating compositions that offer one or more of the following enhanced properties to the coated substrate and/or coating system: chemical resistance, thermal resistance, biological and/or chemical non-stick surface effects, electrochromism, and non-linear optical properties. These and other needs are satisfied by the disclosed coating molecules, coating systems and coating applications.